You can sum the answer up in one word: access.
While there are many unbelievers in the US there are innumerable churches, Christian ministries, magazines, television and radio programs, even entire stations, plus thousands of pastors and, of course, other Christians to reach U.S. unbelievers. Over 1 out of every 4 full time Christian worker in the world lives and serves in the United States.
On the other hand, in many nations there is no, or very limited, access to the gospel – not on television, not on radio, no churches, no Christian publications, absolutely no way to discover who Jesus is. It is estimated that in some areas of the world there is only one Christian worker (a pastor, lay leader, missionary, etc) for every 1 million people.
One missionary, upon entering a village, began talking to a woman about Jesus. She directed him to a shop that could fix his sewing machine thinking perhaps that is what a “Jesus” is and that his was broken.
It is sadly true that there is an abundance of non-believers in the United States but there is also an abundance of believers who can easily make Christ’s name known. There are an endless number of opportunities for a seeker to discover who Jesus is and the message of salvation. We must ask ourselves: Should one group have multiple chances to reject the gospel when there are millions who have never even heard it for the first time?
Finally, Jesus commands us to go – to Jerusalem (or own city), Judea (the surrounding area), Samaria (our neighbors – even if they aren’t very friendly toward us) and the ends of the earth (Acts 1:8). It is not a “pick one” option. He said we were responsible for local and global, Jerusalem and the ends of the earth. Obedience demands we send missionaries. Are you ready to go?
“All authority in heaven and on earth has been given to me.
Therefore go and make disciples of all nations, …